Large valley Nernst effect in twisted multilayer graphene systems

Valley Nernst effect is a newly proposed and experimentally confirmed effect,which could be used to design novel thermoelectric devices.We study the valley Nernst effect in(M+N)-layer twisted multilayer graphene systems by a simple low-energy effective model.It is found that the total valley Nernst coefficient(VNC)is three orders of magnitude larger than that in monolayer group-Ⅵdichalcogenides.The total VNC increases with the increase of layer numbers.It is shown that the total VNC exhibits a structure with three peaks as a function of the Fermi energy.We identify that the central peak is always negative stemming from the flat band.Two shoulder peaks are positively induced by the conduction and valence bands,respectively.These predicted features can be tested experimentally.The present work would shed more light on valley caloritronics.

Electrical and thermoelectric study of two-dimensional crystal of NbSe2

We report experimental investigation of the resistivity and Nernst effect in two-dimensional(2D)NbSe2 crystals.A strongly enhanced Nernst effect,100 times larger than that in bulk NbSe2,caused by moving vortices is observed in thin film.It is found that in the low temperature,high magnetic field regime,pinning effects show little dependence on the thickness and resistivity of the superconductor films.Strong Nernst signals persist above the superconducting transition,suggesting that the Nernst effect is a sensitive probe to superconducting fluctuations.A magnetic field induced superconductor-insulator transition(SIT)is evident,which is surprising in that such a SIT usually takes place in disordered dirty superconductors,while our samples are highly crystalline and close to the clean limit.Hence,our results expand the scope of SIT into 2D crystal clean superconductors.

Electrical and thermal transport properties of kagome metals AV3Sb5(A=K,Rb,Cs)

The interplay between lattice geometry,band topology and electronic correlations in the newly discovered kagome compounds AV3Sb5(A=K,Rb,Cs) makes this family a novel playground to investigate emergent quantum phenomena,such as unconventional superconductivity,chiral charge density wave and electronic nematicity.These exotic quantum phases naturally leave nontrivial fingerprints in transport properties of AV3Sb5,both in electrical and thermal channels,which are prominent probes to uncover the underlying mechanisms.In this brief review,we highlight the unusual electrical and thermal transport properties observed in the unconventional charge ordered state of A V3Sb5,including giant anomalous Hall,anomalous Nernst,ambipolar Nernst and anomalous thermal Hall effects.Connections of these anomalous transport properties to time-reversal symmetry breaking,topological and multiband fermiology,as well as electronic nematicity,are also discussed.Finally,a perspective together with challenges of this rapid growing field are given.